With developments of digital technology and network technology, delivering or selling various items, such as contents and articles, through a network has been rising in recent years. Correspondingly, there are growing needs for technology of providing a user with information about an item on user's desire selected from a number of items. There is disclosed a technology of providing a user with information about items corresponding to user's tastes or interests by user's evaluation information or usage information about items.
Meanwhile, there are great differences between individuals in the continuousness of user's interests against items, rapidity of change in user's tastes and so on, depending on users. Therefore, it is difficult to select and provide appropriate items for a wide range of users. For measures against such a problem, for example, there is disclosed a method of allowing parameters of learning period, recommendation period and numbers of similar users to be established each user thereby recommending contents suitable for the user, in Patent Document No. 1.